The selective catalytic reduction (SCR) of NOx assisted by propene is investigated on Pd/Ce0.68 Zr0.32 O2 catalysts (Pd/CZ), and is compared, under identical experimental conditions, with that found on a Pd/SiO2 reference catalyst. Physico-chemical characterisation of the studied catalysts along with their catalytic properties indicate that Pd is not fully reduced to metallic Pd for the Pd/CZ catalysts. This study shows that the incorporation of Pd to CZ greatly promotes the reduction of NO in the presence of C3 H6 . These catalysts display very stable deNOx activity even in the presence of 1.7% water, the addition of which induces a reversible deactivation of about 10%. The much higher N2 selectivity obtained on Pd/ CZ suggests that the lean deNOx mechanism occurring on these catalysts is different from that occurring on Pd0/SiO2 . A detailed mechanism is proposed for which CZ achieves both NO oxidation to NO2 and NO decomposition to N2 , whereas PdOx activates C3H6 via ad-NO2 species, intermediately producing R-NOx compounds that further decompose to NO and CxHyOz . The role of the latter oxygenates is to reduce CZ to provide the catalytic sites responsible for NO decomposition. The proposed C3H6 -assisted NO decomposition mechanism stresses the key role of NO2 , R-NOx and CxHyOz as intermediates of the SCR of NOx by hydrocarbons.